code: def test_substitute(self):
      aug = naa.LoudnessAug()
      augmented_data = aug.augment(self.audio)
      augmented_audio = augmented_data[0]
  
      self.assertFalse(np.array_equal(self.audio, augmented_audio))
      self.assertEqual(len(self.audio), len(augmented_audio))
      self.assertTrue(self.sampling_rate > 0)
  
file_path: nlpaug/test/augmenter/audio/test_loudness.py
imports: import unittest
  import os
  import numpy
  from dotenv import load_dotenv
  import nlpaug.augmenter.audio
  from nlpaug.util import AudioLoader
label_desc: Use image node_id 3 for calling the TestLoudness obj's underlying member method code with example usage: obj.test_substitute() without return types